Would you be likely to work out more if you didn’t have to pay upfront for a gym, and the cost per class decreased the more you attended? How about if you could find and reserve classes in your area via a smartphone app? How about if the classes were called “Twerkout Conditioning” and “Weapons of Ass Reduction?”

Fitmob CEO Raj Kapoor

Launching today, Fitmob is a new startup that combines the elements of a would-be fitness craze with the dynamics of a mobile marketplace.

The company was co-founded by two Silicon Valley types — a venture capitalist and an engineer — and Tony Horton, the energetic infomercial star who created the popular video workout series P90x.

From Horton, who is not involved in day-to-day operations, the company got the idea of using body weight fitness and the motivation of “how can you make it more like a party?” said Fitmob CEO Raj Kapoor, who founded the photo site Snapfish before he was a VC.

Kapoor and co-founder Paul Twohey (formerly of recommendation app Ness and Palantir) have raised $6.5 million from Mayfield, plus $3.25 million from Silicon Valley Bank, and have a full-time team of 13 in San Francisco. They aim to tackle the $75 billion global health club market, where some estimate that more than half of memberships go unused.

In some ways, Fitmob is barely a tech startup. It holds fitness classes in its office. It only offers about 10 different classes, and only in San Francisco. It does have an app (iOS only).

But there are some deeper themes, too, according to Kapoor. “Ninety percent of an online-to-offline business like Lyft or Uber is offline,” he argued. “These are really service businesses.”

From Kapoor’s experience as a board member at Lyft, via his previous gig at Mayfield Capital, he got the inspiration to create a community around the marketplace, with plans to hand out piles of brightly colored t-shirts, make sassy workout classes around themes like twerking, and send notifications to friends when users sign up for or drop out of classes.

Kapoor also said he likes to think of Fitmob as a sharing economy startup, with the promise of changing the dynamic of paying upfront for gyms by connecting the largely underutilized and underpaid personal trainers of the world to new students.

But that’s not exactly true, yet. For now, Fitmob has just five personal trainers in its system and is deeply involved in planning curricula and booking locations.

Perhaps the real test will be whether Fitmob can appeal to a lot of people (not everyone’s fitness aspirations are “a twerk that’d silence Miley Cyrus”) and whether it can harpoon the elusive fitness white whale: Long-term motivation.

If you look past all the party rock, the price structure may be the real hook: $15 per class, or $10 if you attend two per week, or $5 if you attend three.

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